RU2475460C2 - Method of processing puzzolanes - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention may be used for making concrete mixes, mortars and other mixes containing cement. Method of processing puzzolanes including slag and flue ash such as Class F and/or Class C comprises subjecting puzzolanes to high-intensity grinding in appropriate grinders. Note here that low-density hollow particles as larger particles of slag get decomposed to activate surface of said particles to make finished product feature the following distribution of particles by sizes (in wt %): ≤5 micron - 15-25, ≤10 micron - 30-40, ≤30 micron - 90-95. Invention is developed in its subclaims.

EFFECT: higher activity of puzzolanes and strength of construction materials.

7 cl, 3 tbl

Description

The present invention relates to a method for processing pozzolans in the form of fly ash.

Fly ash is used for the production of concrete mixtures, mortars and other mixtures, including cement. Fly ash is a waste from the production of solid fuel power plants, and it is produced in huge quantities every year around the world.

The present method allows to eliminate fluctuations in the quality of fly ash caused by differences in the chemical compositions of coal and the parameters of coal combustion processes. The processing of pozzolans, that is, fly ash, in accordance with the present method significantly improves the performance of concrete and allows a greater degree of replacement of standard Portland cement, which leads to significant economic and environmental benefits.

Fly ash usually contains about 85% glassy amorphous components in the form of cenospherical particles. According to ASTM C 618, fly ash is divided into two classes Class C and Class F. Fly ash Class F usually contains more than 70% by weight of silica, alumina and iron oxides, while the content of these components in the ash is Class C ablation typically ranges from 70% to 50%. Class F fly ash is generated as a waste from the burning of bituminous coal. The fly ash Class C has a higher calcium content and is generated as waste when burning semi-bituminous coal.

According to the American Coal Ash Association, in 2006, the United States produced about 73 million tons of coal ash in the form of fly ash and only about 45% was used in various industries, while the remainder was mainly stored at landfills for waste disposal. Currently, in the US, Portland cement replacement in concrete is only 10 percent.

An exhaustive study showed that concrete mixtures with a high amount of fly ash, in which Portland cement was replaced with fly ash to a content above 50%, are characterized by a higher increase in long-term strength, reduced water permeability and gas permeability, high resistance to chloride ion and so on in comparison with Portland cement concrete mixtures without fly ash.

However, concrete with a high content of fly ash has significant disadvantages. One drawback is the very long setting time and very slow build-up of strength over a period of 0 to 28 days, especially when the ratio of water to binder is higher than 0.50. These negative effects reduce the use of fly ash to replace Portland cement by an average of 15–20%.

Serious problems also include the problem of the stability of the quality of fly ash. Typically, deviations in the chemical composition of the coal used and frequently changing parameters of the operation mode of the boilers cause the formation of crystalline and quasicrystalline phases, the so-called slags, which leads to a decrease in the reactivity of fly ash expressed by the so-called pozzolanic activity.

Several attempts have been made to improve the performance of concrete mixtures with high fly ash, see, for example, Malhotra, Concrete International J., Vol. 21, No. 5, May 1999, pp. 61-66. According to this publication, the increase in the strength of such concrete mixtures could be improved by significantly increasing the content of the binder, i.e. cement and micro-filler, and greatly reducing the amount of water, but this approach requires the use of an increased amount of plasticizing additives to maintain an acceptable consistency of concrete mixtures, which dramatically increases concrete cost.

A number of methods have been developed relating to grinding fly ash to increase its pozzolanic activity by grinding, which increases the number of particles of fly ash with a size of about 11 microns, and the simultaneous introduction of calcium oxide. Such methods are described in US patent documents No. 6818058, 6038987, 5714002, 5714003, 5383521 and 5121795. All of the known methods either can not provide a significant improvement in the performance of fly ash as a component of concrete, or cannot prevent fluctuations in the properties of fly ash and guarantee consistent quality of the finished product.

The present invention solves these problems.

Therefore, the present invention relates to a method for processing pozzolans, including fly ash, such as Class F and / or Class C fly ash, used for the preparation of mortars and concrete mixtures, characterized in that the pozzolans are subjected to high-energy machining by grinding in equipment for grinding to a particle size of the finished product, characterized by a retention of less than 5% on a sieve with a hole size of 30 microns, resulting in particles of pozzolan receive mechanical impulses, at which s are not disintegrate cenospheres coarse particles of slag, and whereby the surface is activated tsenosfernyh ground particles.

The present invention can be carried out using various types of grinding equipment, such as grinding equipment using media, for example, stirred, centrifugal, ball; or grinding equipment that does not use media, such as inkjet, impact, roll, with the prevailing mechanical shear pulses applied to the particles to be treated, and combined with air classification.

According to a preferred embodiment of the present invention, pozzolan is pre-screened to separate a fraction with a retention of at least 90% on a sieve with a mesh size of 45 microns, and in which larger particles are crushed to a particle size with a retention of less than 5% on a sieve with a hole size 30 microns, to achieve strength according to the pozzolanic index ASTM C 618 after 28 days, which is ≥75%.

According to another preferred embodiment of the invention, the pozzolan is pre-screened to separate the fraction with a retention of at least 95% on a sieve with a hole size of 45 microns, and in which larger particles are crushed to coarseness with a retention of less than 5% on a sieve with a hole size 30 microns.

According to another preferred embodiment of the invention, the pozzolan is pre-screened to separate the fraction with retention of at least 99% on a sieve with a mesh size of 45 microns, and in which larger particles are crushed to coarseness with a retention of less than 5% on a sieve with a size holes 30 microns.

According to another preferred embodiment of the invention, the pozzolan after said preliminary screening is subjected to co-grinding to a particle size characterized by a retention of less than 5% on a sieve with a hole size of 30 microns.

According to a much more preferred embodiment, the pozzolan is ground so that the finished product has the following particle size distribution:

≤5 microns 15-25 wt.%,

≤10 microns 30-40 wt.%,

≤30 microns 90-95 wt.%.

The pozzolan treated according to the invention can be further processed by adding Portland cement. According to one preferred embodiment of the invention, Portland cement is added to said pozzolan in an amount up to 10% by weight during or after said processing of pozzolan.

It is also preferred that plasticizing additives, setting time adjusters and / or strength improvers are added to said pozzolan in powder form during or after said pozzolan processing.

The main advantage of the present invention is that the proposed treatment of fly ash minimizes the effects of fluctuations in the composition of coal and the conditions in the boiler on the properties of fly ash. Another advantage is the ability to increase the replacement of Portland cement in concrete, which significantly reduces dry gas emissions and energy consumption associated with the production of Portland cement.

Examples

Tested in accordance with this invention, fly ash Class F in accordance with ASTM C standard with chemical composition and particle size distribution (PSD) are shown in tables 1 and 2.

Table 1
Chemical composition Compound Fly ash Cao 15.0% SiO ₂ 49.4% Al ₂ O ₃ 19.6% Fe ₂ O ₃ 5.2% SO ₃ 0.8% Na ₂ O 0.3% K ₂ O 1.2%

table 2
Particle size distribution Parameter Fly ash The average particle size (microns) 15,2 Maximum particle size (μm) 120 Detained by a 325 mesh sieve. (45 μm),% 22

Table 3 below shows the data on the increase in strength according to ASTM C 109 mixtures of 50/50 by weight of Portland cement (type 1 according to ASTM C 150) and additional mineral binders (SCM), not subjected to processing and subjected to processing according to the present invention.

Table 3
The increase in compressive strength, MPa (psi) Type of mineral binders (SCM) Curing time, days one 3 7 28 1. Not processed slag after dispersion (95% of large particles of 45 microns) 2.5 (364) 4.3 (630) 5.8 (842) 9.0 (1315) 2. Treated slag after dispersion (95% less than 30 microns) 6.6 (962) 14.3 (2079) 20.1 (2903) 28.7 (4158) 3. Processed fly ash with treated slag (finished product 95% less than 30 microns) 8.8 (1269) 19.1 (2769) 27.0 (3911) 35.2 (5108) 4. A mixture of 50/50 type I cement and blast furnace slag (Blaine specific surface area 4000 cm ² / g) 25-28 MPa 30-38 MPa

The test results show that the present invention allows you to convert a completely inert fraction of large particles of fly ash with zero pozzolanic activity into a reactive fraction, which leads to a significant increase in strength. Additive cement containing 50% Portland cement and 50% fly ash treated according to the present invention showed a strength of 35-40 MPa at a curing time of 28 days, which corresponds to the average strength achieved for type I cements and its mixtures 50 / 50 with high quality blast furnace slag.

In addition to the significant performance benefits associated with high wear resistance, and so on, the present invention also provides an important environmental effect associated with the possibility of using low-level ashes for concrete production, which are usually disposed of as landfill in landfills.

Several embodiments of the invention have been described above. However, the present invention is not limited to the examples of embodiments described above, and may be modified in the claims.

Claims (7)

1. A method for processing pozzolans, including slag and fly ash, such as Class F and / or Class C fly ash, used for the production of mortars and concrete mixtures, in which the pozzolans are subjected to high-energy mechanical processing by grinding in grinding equipment, in resulting in particles of pozzolan receive mechanical impulses, characterized in that non-cenospheric particles in the form of large particles of slag disintegrate, and as a result, the surface of the coenospheric ground particles is activated, and zsolan is subjected to grinding, so that the finished product has the following particle size distribution:
≤5 μm 15-25 wt.%,
≤10 μm 30-40 wt.%,
≤30 μm 90-95 wt.%. 2. The method according to claim 1, characterized in that the pozzolan is subjected to preliminary screening to separate the fraction with retention of at least 90% on a sieve with an opening size of 45 μm, and larger particles are crushed to a particle size with a retention of less than 5% on a sieve with a hole size of 30 μm to achieve strength in accordance with the pozzolanic index ASTM C 618 after 28 days, which is ≥75%. 3. The method according to claim 1, characterized in that the pozzolan is subjected to preliminary screening to separate the fraction with retention of at least 95% on a sieve with a hole size of 45 μm, and larger particles are crushed to a particle size with a retention of less than 5% on a sieve with a hole size of 30 microns. 4. The method according to claim 1, characterized in that the pozzolan is subjected to preliminary screening to separate the fraction with retention of at least 99% on a sieve with a hole size of 45 μm, and larger particles are crushed to a particle size with a retention of less than 5% on a sieve with a hole size of 30 microns. 5. The method according to any one of claims 1 to 4, characterized in that Portland cement is added to said pozzolan in an amount of up to 10% by weight during or after said pozzolan processing. 6. The method according to any one of claims 1 to 4, characterized in that plasticizing additives, setting time adjusters and / or strength improvers are added to said pozzolan in powder form during or after said processing of pozzolan. 7. The method according to claim 5, characterized in that plasticizing additives, setting time regulators and / or mixtures are added to the indicated pozzolan, which increase the strength in powder form during or after the specified processing of pozzolan.